The present invention relates to air ventilation and an improved air ventilation system which includes the capability of adjusting air pressure within the conditioned space.
ANSI/ASHRAE Standard 62-1989 was established to address the need for increased ventilation of buildings due to poor indoor air quality. Increased levels of contaminants from humans, fuel burning appliances, building materials and furnishings have resulted from current construction practices which produce tighter, low leakage buildings. For example, volatile organic compounds (VOCs) such as formaldehyde have been identified. Continued exposure to VOCs can cause illness. Recommended ventilation rates range from about 0.3 air changes per hour to over 1.0 air changes per hour. The actual level of recommended outdoor air intake depends on the use, size and occupancy of the building.
Homeowners also are becoming more aware of the importance of including air ventilation systems within their homes. In recent years, there is an increasing move toward houses with higher air tightness. Due to insufficient natural ventilation, however, air fouled with tobacco smoke and poisonous emissions from gas burning devices tend to stagnate inside homes. In addition, unless ventilation is sufficient during rainy seasons, dew may be formed on walls, thereby inducing growth of mold. Insufficient ventilation is therefore unsanitary. There exists a need for smaller, less complex, less expensive ventilation systems that are appropriate for residential use.
An additional problem associated with air-tight homes concerns differences in air pressure inside and outside the home. When ventilation systems are installed the builder typically ensures that the system draws as much air into the building as the system removes, thereby keeping the air pressure inside balanced with the air pressure outside. However, problems arise when the inhabitants activate other ventilation systems within the home such bathroom and kitchen fans. When these devices are activated they can produce a pressure drop inside the home and can potentially accumulate harmful gases such as carbon monoxide from open-flame combustion devices like furnaces and stoves. This potentially deadly back-draft of harmful gases could be avoided if the ventilation system could draw in more air than it takes out in order to make-up for other systems removing air from the space.